The invention relates to a hub or pulley of sheet metal made by spin-roll forming, but more particularly, the invention relates to a pulley having a hub spun-roll formed by radially displacing an annular sheet metal disc outward from a bore.
Machined hubs formed from bar stock are sometimes attached to webs and rims formed of sheet metal to make pulleys. A sheet metal web (or disc) and rim are attached to a machined hub be welding, brazing, fasteners, or adhesion. A machined hub may provide complicated shapes such as a closed bore but it introduces the attendant problems of weight, cost and process complexities associated with axially alignment during assembly of the hub to the rim.
Hubs or pulleys of sheet metal may be shaped by press forming using a series of dies or spin-forming using mandrels and rollers or a combination thereof. For example, a pulley with an integral hub that is press formed is disclosed in U.S. Pat. No. 5,441,456 with a stepped bore in FIG. 5, and a bore with spline receiving grooves in FIG. 8. Belt receiving grooves are spin formed in the rim of the pulley. Another pulley with an integral hub is shown in U.S. Pat. No. 4,824,422.
German Patent No. 4,444,526 discloses a method of shaping a hub by spin forming where a shaping roller is pressed against a side of a spinning annular disc of sheet metal that is supported at an opposite side with a head stock mandrel. The shaping roller is moved progressively radially inwardly against the side of the rotating disc which displaces a portion of metal while thinning part of the disc and forming a sidewall having a thickness that is less than the original sheet metal thickness. An annular wave is formed as metal is displaced and which progressively, axially extends. A shaping roller presses the annularly displaced metal against a mandrel while simultaneously forming a hub integral to the disc. The problem with such hubs is that the formed hub sidewall is formed from one side of the hub only. In addition, in order to form such hubs, a greater amount of metal is displaced, as such, hubs requiring a smaller outside diameter are more difficult to form.
A hub having a bore, in accordance with the present invention, is spun-roll formed of a portion of an annular sheet metal disc. The hub is formed by radially displacing a portion of the annular sheet disc outward from the bore. The so formed hub that is integral to the annular sheet metal disc forms a web having a thickness equivalent to or not less than a thickness of the annular sheet metal disc before formation of the hub. The web may be used to spun-roll form a rim having a belt receiving portion and as such a one-piece spun roll formed pulley. The web may also be used to interconnect to a rim having a belt receiving portion as a separate piece from the hub and web.
During the spinning process, a shaping roller is pressed against a bore of an annular sheet metal disc which is being rotated simultaneously. The shaping roller is moved progressively, radially outward, with or without axial oscillation, against the bore of the rotating disc which displaces a portion of metal in the form of an axially extending collar. The shaping roller include various surface configurations for forming any number of various hub shapes. In addition, the spinning process may include the use of more than one shaping roller acting on the annular sheet metal disc at different times.
An object of the invention is to provide a hub that is spun-roll formed by radially displacing a portion of an annular sheet metal disc outward from a bore. The invention provides an ease of manufacturing by reducing complexities associated with axial alignment. Further, the invention affords the ability to produce smaller compact hub and pulleys.
Another object of the invention is to provide a method of spin forming a hub with an integral web having a thickness which is unchanged after the spin forming process and as such stronger.